Thread: Thinning with TPDRA

How do you mean "will not need further sanding"?

Whatever the epoxy, before putting anything else over it, you will need to sand it.
Come to think of it, with 3 coats already in place, why do you need to put another coat on at all ?

cheers
AJ

Better than tipping off is dragging the roller to get a smooth surface. Saves a brush, is faster and does a better job.

You will need to sand after for the paint or varnish to go over the top.

The TPDRDA won't do anything really bad ... but it will make the final surface a little bit softer.

MIK

Originally Posted by b.o.a.t.

How do you mean "will not need further sanding"?

Sorry, I meant will not need extensive sanding.

When I started using epoxy, even the stuff I was just using a soak coat, I didnt tip it off, meaning that I ended up with a heavy roller texture and sometimes runs. This took quite a bit of sanding to remove. I was trying to avoid that.

Originally Posted by b.o.a.t.

Whatever the epoxy, before putting anything else over it, you will need to sand it.

I had forgotten that I need to do a light sanding regardless of how smooth the final epoxy coat is. Disaster averted. Thanks.

Originally Posted by b.o.a.t.

Come to think of it, with 3 coats already in place, why do you need to put another coat on at all ?

You will probably remember the post that I did about my various disasters applying the fibreglass. The first coat was the TPDRA-thinned one I did before putting the glass on. Then I needed to move the glass, distorting the weave as it stuck to the wet hull. I then applied two coats of neat epoxy over the glass. The substantial distortions to the glass weave gave me some way-too-big wrinkles. I then sanded heavily. In some cases I cut through the glass where the wrinkles were, which didnt worry me greatly as they were high up on the sides and where the glass was probably not needed anyway. That left me putting on the fourth coat. With my patience with sanding gone completely, I wanted to do a coat that didnt require extensive sanding. Hence the question.

remember, I'm a begginer, so dont expect me to be starting from a well thought out position.

cheers and thanks
Arron

Originally Posted by Boatmik

Better than tipping off is dragging the roller to get a smooth surface. Saves a brush, is faster and does a better job.

You will need to sand after for the paint or varnish to go over the top.

The TPDRDA won't do anything really bad ... but it will make the final surface a little bit softer.

MIK

Thanks MIK. Early this morning I applied a TPDRDA thinned coat over the hull. It looks wonderful. It quite smooth too - I think with a light sand I'll be quite happy with it.

There is one thing though - there seems to be lots of tiny bubbles. These didnt seem to be there when the coat was applied, so must be arising after. I was wondering if they were caused by the wood outgassing but they are on top of three layers of epoxy so I guess not. I also put a coat on an old canoe with a heavily painted surface and its doing the same thing.

The bubbles dont worry me greatly, I dont think they create a risk of water egress or anything - but I'd like to know where they came from to avoid them next time ?

thanks
Arron

Arron, do yourself a favour and get rid of the thinners. Just toss them in the bin. All they do is cause complications of one sort or another and while it's fine for the experts to be totally honest and point out where the things can be used safely or with minimal problem, they are also too honest to come straight out and say ... YOU DON'T NEED THEM!

That's the bottom line mate.

Sure, the thinners might be helping a bit now, but with a teeny bit of practice, you can get perfect finishes with unthinned poxy. The same goes for any of the other uses for thinned poxy.

Remember, everytime you add thinners, you're creating the possibility of small worm holes that allow the ingress of water. Everytime you use thinners, you've added another step to the process complete with opportunities to stuff up. Every time you use thinners, you've spent money on a product (that you don't need).

People will argue about technical uses for the stuff but the reality is: YOU DON'T NEED IT!

So do yourself a favour and save this tin for cleaning brushes, then never buy it again.

That's the heretic's advice, one muggins to another - Mik and PAR have a responsibility to give you the full story, I don't, I only need to advise from my moaning chair (the place we go when we stuff up). Seriously mate, you're making this boating caper too hard. I know, I was there as Mik will attest, but this boat building caper is a stupidly simple game once you get the hang of it. Too many amateurs think that you improve the experience/product by complicating it. You don't, you only complicate it. Professionals like Mik and PAR do, on occasion, use stupendously complicated techniques and commit outrageous acts of sorcery in their boat buiding, but that's because they were forced to by the demands of the job at hand - you can bet that both of them use the simplest method available to achieve the result they need.

Richard

The tiny bubbles was the thinner leaving the epoxy (flashing off). This is a form of out gassing, but has nothing to do with the wood. The vapor pressures exceeded the ability of the resin viscosity to restrain the gasses until cured. Had the vapor pressure of the solvent been lower, you may not have had bubbles pop on the surface, but they'd still be there under the surface. If you wave a heat gun or my usual tool a blow torch, over the surface during the first part of the cure, you'll pop the bubbles and most of the time the epoxy will flow out and fill the divots. Of course both thinning and using a torch are poor epoxying procedure and can lead to other issues.


I will not get into the thinning epoxy debate, as I think everyone pretty much knows my feeling about it. I will say, unless you have a full grasp of the chemistry involved with epoxy, screwing around with it's makeup is folly and ultimately it's using your boat finish as a test bed for the latest chemical formulation. As a rule, particularly high vapor pressure solvents (TPDRDA, keytones, toluene, alcohols, etc.) shouldn't be mixed with epoxy in normal boat building procedures.

TPRDA is not a .... just thinking how to phrase this ... because I am not really clear on what it is ...

Forgive me If I get it wrong in a technical sense.

TPRDA is not a hydrocarbon solvent like the others ... it is meant to stay in the epoxy matrix. I don't think it is particularly useful, but I dont think it does much harm either.

I should be more specific ... I don't think it is useful for new construction (or harmful) and is caught up in the mistake that the "epoxy has to soak in". If that was the case we would have to add it to glued joints too - which the manufacturers advise against. So if it sticks in a joint .. it is going to stick to a surface.

The bubbling is unexpected to me too. I've never used it for a last coat.

The bubbling doesn't concern me too much either, but I am more worried about bubbling than I am about sanding. So would probably leave out the TPRDA next time.

BTW ... was there direct sunlight on the areas on which you put it?

BTWBTW ... I think it is quite useful in repair work where timber has gone a little "soft" but has not rotted sufficiently to merit pulling it out. There the improved soaking with added TPRDA is useful.

Best wishes
Michael

I'll be happy not to use (and therefore pay for) TDPRA any more.

The boat was in the garage, there was no direct sunlight.

Arron

It remains a mystery to me then ... thought it might just be possible that it was outgassing (hate that word .. like some mysterious gas ... it is just expanding air) from the sanded glass areas.

Anyway ... you have done a good job so don't worry about it.

Best wishes
MIK

My understanding is it's a "wetting agent" which thins out the epoxy, permitting better penetration. I would suspect they use it to decrease "surface tension" in the matrix.

The Bote Coat people say it's a reactive modifier, but don't go further into it's description. I can only think of a few ways to do this chemically and assumed it was a solvent in my previous post.

If someone on working terms with them, could find out more specifics on what it is, I'd appreciate it.

Just noticed this on the TPRDA bottle

'as it is an all solids formulation it does not contain solvents which will evaporate and leave pin holes'

I haven't experienced it myself but I have heard of bubbles appearing due to tiny air bubbles in the epoxy expanding as the epoxy warms. This seems like a possible cause as you applied the epoxy in the morning, have you tried applying it in the evening so that it cools as it sets?

When the thermolidic reaction takes place, the epoxy warms, but there would have to be air trapped for bubbles to form. In other words, Boat Coat, like most good epoxies is 100% solids, meaning that there isn't anything left over from the reaction (unlike polyester for example). If everything is involved in the matrix, then what forms the bubbles?

This means the bubbles were "introduced" to the matrix and took a while to rise to the surface and appear. Common causes of bubbles are aggressive mixing and brushing or excessive pressure under an applicator or squeegee. Again, these can be removed with a heat gun or torch, waved over the surface (don't stop, keep it moving, trust me).

Wow ...the forum really doesn't want to accept my answer.

I've written two so far.

Bote Cote, quite reasonably, are quiet about what the TPRDA is.

My observation is that it has no smell, or very little (showing it doesn't evaporate much). It reminds me of glycol just a little but I am pretty sure it in not glycol.

It needs some way of bonding with the epoxy .. which could mean hydroxyl groups available to react with the 'pox (that's why epoxy bonds with timber - because timber has hydroxyl groups on the cellulose) - but my memory (and depth) of chemistry is oh too far away now.

MIK